1. Field of the Invention
The present invention relates to the papermaking arts. More specifically, the present invention relates to a seam assist device for pulling together and aligning two ends of a papermaker's fabric for seaming on a paper machine.
2. Description of the Prior Art
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
Woven fabrics take many different forms. For example, they may be woven endless, or flat woven and subsequently rendered into endless form with a seam. Woven fabrics are typically in the form of endless loops, or are seamable into such forms, having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross. Because paper machine configurations vary widely, paper machine clothing manufacturers are required to produce fabrics, and other paper machine clothing, to the dimensions required to fit particular positions in the paper machines of their customers. Needless to say, this requirement makes it difficult to streamline the manufacturing process, as each fabric must typically be made to order.
Fabrics in modern papermaking machines may have a width of from 5 to over 33 feet, a length of from 40 to over 400 feet and weigh from approximately 100 to over 3,000 pounds. These fabrics wear out and require replacement. Replacement of fabrics often involves taking the machine out of service, removing the worn fabric, setting up to install a fabric and installing the new fabric. While many fabrics are endless, about half of those used in press sections of the paper machines today are on-machine-seamable. Some Paper Industry Process Belts (PIPBs) are contemplated to have an on machine seam capability, such as some transfer belts, known as Transbelt®. Installation of the fabric includes pulling the fabric body onto a machine and joining the fabric ends to form an endless belt.
In brief, the seam region of any workable fabric must behave under load and must have the same permeability to water and to air as the rest of the fabric, in order to prevent the periodic marking of the paper product being manufactured by the seam region.
Despite the considerable technical obstacles presented by these requirements, it is highly desirable to develop seamable fabrics, because of the comparative ease and safety with which they can be installed.
To facilitate seaming, many current fabrics have seaming loops on the crosswise edges of the two ends of the fabric. The seaming loops themselves are formed by the machine-direction (MD) yarns of the fabric. A seam is formed by bringing the two ends of the fabric press together, by interdigitating the seaming loops at the two ends of the fabric, and by directing a so-called pin, or pintle, through the passage defined by the interdigitated seaming loops to lock the two ends of the fabric together.
Alternatively, a monofilament seaming spiral may be attached to the seaming loops at each of the two ends of the papermaker's fabric. The monofilament seaming spirals are connected to the seaming loops by at least one connecting yarn. The coils of the spirals at the two ends of the fabric may then be interdigitated and joined to one another on the paper machine to form a seam usually referred to as a spiral seam.
In a so-called warp loop seam, the rows of loops are formed of extended edge loops of warp yarns in the fabric structure of the fabric. In a so-called spiral seam, each row of loops is instead formed of a separate, preformed yarn spiral, which is extended along and attached by means of a CD pintle connecting the spiral, intermeshed with the machine direction yarns, such as warp yarns, to the seam edge of the fabric. Alternatively, the spiral can be attached to the clothing by a number of cross-machine direction yarns being raveled a distance from the seam edge, whereupon the loops of the spiral are inserted into the thus formed looser edge portion. Then the edge is folded back over itself and is attached to the clothing, for instance, by using a sewing machine. Independently of how the spiral is attached, the clothing comprises two spirals, one along each seam edge, which, when joining together the fabric, are meshed with each other like a zipper so as to be joined together by means of a pintle wire or the like.
Alternatively, fabrics can be formed completely of spirals as taught by Gauthier, U.S. Pat. No. 4,567,077; which is incorporated herein by reference. In this case, the spirals are connected to each other by at least one connecting pin. In theory, the seam can therefore be at any location in the fabric body where a connecting pin may be removed. The best known advantage of a spiral fabric versus a woven fabric is the seam is geometrically similar to the fabric body.
A seam is generally a critical part of a seamed fabric, since uniform paper quality, low marking and excellent runnability of the fabric require a seam which is as similar as possible to the rest of the fabric in respect of properties such as thickness, structure, strength, permeability etc.
An important aspect of seaming a fabric on a paper machine is that there be uniform tension across the fabric. If uniform tension is not achieved and one section of the fabric pulls more than another, then the fabric can bubble or ridge across the fabric width.
Another aspect of seaming a fabric is preventing damage to the fabric body. In order to avoid or minimize the chance of damage to the fabric during installation, non-uniform tension, weight and pressure must be avoided on the seam itself.
It has been common practice to attach zippers and VELCRO®or hook and loop type assists to fabrics by use of staples, sewing and/or adhesive materials. However, since these attachment methods can damage the fabric surface, it is preferable to use methods which do not damage the fabric.
A further aspect of seaming a fabric, especially very long ones is properly aligning the fabric body in the machine so the fabric guides true in the machine direction and does not oscillate or track to one side of the machine. If the fabric guides or tracks poorly it can make contact with the paper machine support frame and cause fabric damage.